I also recently switched over to OSx from Windows/Linux. Man, what a difference. I used to hate all the freaking Mac jokers that were overconfident about how their stupid computer ran, well, guess what.........It runs that good.
So, Windows on OSX. I use a program called Parallels (http://www.parallels.com/en/products/desktop/). The biggest thing I use it for is MS Streets and Trips & Chief Architect. The latter is a program I use to build houses. MS Streets has a USB GPS device and it works fine as does the USB key for Chief.
Also, Windows runs flawlessly, although to be honest most of what I do does not require a lot of ram and, on top of that I have 2gigs of RAM in my laptop. I first started with 512MB RAM and I just wanted to die; but I think 1gig should do for most application.
Transferring files is a breeze, getting on the network anything you want to do should work.